ADSL router & windows server 2003

I currently have a setup with one Windows server 2003, clients running w2k or w98 and an ADSL router.
Currently they are all using the router as a gateway to the net, what i want to do is have the internet routed through the server then to the clients so the server is directly connected to the internet and so i dont have to configure port forwarding to the server, it could also allow better security.
the Router has USB & ethernet but it is not practical to connect it to the server via usb because they are in different parts of the building.
so basically Router <====> Server <----> clients instead of Router <----> everything.

Thanks for reading 🙂